We feel airborne chemicals when they stimulate nerve endings in the eyes, nose, mouth, and throat. Government regulators view chemical irritation as a material impairment of health, and set many exposure limits accordingly. Basic data on sensory response to chemicals are vital for setting exposure-limits and for understanding the relationship between sensation and physiology. However, basic data are scarce, particularly in humans. Data on the effects of stimulus-duration are especially scarce. Sensory systems can integrate stimulus-energy over time to detect weak stimuli (temporal integration). Thus, one must study the domain of time to fully understand any system. Aim 1 a will examine integration in detection of nasal irritation for presentations that last up to several seconds. Short-term integration is important because much of the data on nasal irritation are based on brief exposures. For fixed concentrations, duration will vary to find the briefest pulse that causes perceptible irritation. So far, a simple but imperfect mass-integrator model fits plots of threshold-duration vs. concentration quite well. The experiment will test the hypothesis that simple but imperfect integration is common for other compounds. Aim 1 b will examine integration that occurs up to one minute, using pulsed stimulation with a rhythm similar to natural breathing. The research will test the hypothesis that integration occurs across "breaths," and can allow subjects to detect nasal irritaiton at lower concentrations than brief exposures would suggest. The studies will provide pilot data for more detailed studies that ask whether brief presentations can predict longer-term integration, such as might occur in natural environments. Aim 2 will test a new model of short-term integration based on transport of molecules. In the model, subjects perceive irritation when concentration in nasal tissue reaches a critical level. Concentration builds (integration occurs) as molecules diffuse into tissue from the air. However, diffusion out of tissue into the bloodstream undermines build-up. The model will be tested using using dynamic stimuli, i.e., pulses of irritants interupted by gaps of clean air. The model predicts that interrupting inflow into the mucosa will degrade detection by allowing diffusion out of the mucosa progress unchecked. The three experiments will lay groundwork for a psychophysics of dynamics that can help physiologists understand underlying mechanisms and policy-makers predict how our dynamic sensory systems will react over time. [unreadable] [unreadable] [unreadable]